When Greta Ossman climbed into her attic to install some wiring last summer, she discovered why the energy bills for her Sacramento home had been so expensive.

"Someone, sometime, had knelt on my main heating and cooling duct," Greta explained. "You could see the knee-print on the crushed duct, and it had pulled away from the connector. All this cold air I needed in the house was spilling into the attic."

After the leaking duct was repaired, Greta's electricity bill fell substantially, and her home was much more comfortable.

A new California law that goes into effect next month will make it easier for homeowners to discover such energy-wasting problems.

Beginning October 1, 2005, homeowners living in most of California who install or replace a central furnace or air conditioner must have their ductwork Ñ those flexible tubes that carry the conditioned air throughout the house Ñ tested for leaks. Duct systems that leak 15 percent or more must be sealed to reduce the leaks.

"In most of California, the greatest use of energy is for air conditioning and heating," said California Energy Commission Vice Chair Jackalyne Pfannenstiel. "New air conditioners and furnaces are much more energy efficient and will save you money. It makes no sense to invest in a new air conditioner or furnace, however, unless you are sure that your ducts are working properly and the conditioned air is actually going to get to the rooms."

Often that air winds up in the attic or under the house instead of where it's needed. According to independent research, the duct system in the average California home leaks around 30 percent. That means 30 cents of every heating or cooling dollar is wasted, and the figure can be worse Ñ poorly sealed ducts that leak 70 percent or more are not uncommon.

In most parts of the state, homeowners need a permit to replace or install furnaces or air conditioners. Under the new law, once a contractor installs the equipment, he or she must test the ducts and fix any leaks that are found. Then an approved third-party field verifier must check to make sure the duct sealing complies with the requirements. The homeowner can choose whether the field verifier checks the ducts in the homeowner's house, or their house is included in a random sample where one in seven homes have their duct systems checked.

"Simply put, this new law means that homeowners will now know if their ductwork is properly delivering the benefits of that new compressor or furnace, and not just dumping heated or cooled air into the attic," said Vice Chair Pfannenstiel.

The Energy Commission estimates that duct testing and sealing should cost homeowners, on average, about $660, although the price will vary depending on the condition of the ductwork. The resulting energy savings will more than pay for the added cost, and the benefits of the new law will become even more important this winter; Hurricane Katrina severely damaged important natural gas fields in the Gulf Coast. As a result, natural gas is in tight supply around the country. The United States Department of Energy predicts natural gas prices could increase as much as 70 percent this winter; in California, natural gas utilities are predicting increases upwards of 40 percent.

"During the California energy crisis of 2000 and 2001, some homeowners reported bills of $200 to $300 per month, just for natural gas," said Vice Chair Pfannenstiel. "With utility bills, unlike the posted prices at the gas pump, you don't see the cost on your bill until a month or two later. By the time you get the bill, it's too late to conserve."

More information on "the Changeout law" is available on the California Energy Commission's website at